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Sandpaper is very good for rounding things off, but that isn't what you want to do with the feet of a bridge. I try to only use sandpaper on places I want to round this off (like the top).

You should make a wood spacer to spread the feet a little bit and to stabilize them before you start. Not much, only a mm or two. With a bass bridge, I hold the bridge where I want it, at the proper angle, and then mark the curve onto the bridge on both sides with a pencil sharpened so it rests near the bridge and as far off the top as I want to trim the bridge. I cut close to that line with a bandsaw, but you should be able to get it down with a knife fairly quickly.

Use a sharp knife and remove wood everyplace that touches. If you have a jig that can hold the bridge at the same angle every time then that will really help. Keep taking only little pieces of wood at a time. Cut from the outside towards the inside to keep from taking too big a chunk out. A sharp curved blade is a must! When you are really close, then you can hit it with the sandpaper or rub it over carbon paper to see where the high parts are.

If your bridge fits good, then it will pop into one spot and stay there. If you sand it then it will probably rock back and forth and you will have a warped bridge that always wants to move towards the fingerboard.

When you are done you will either sigh a big relief that you were finally able to finish this job 3 days later, or you will wish you had just paid someone else to do it!

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It seems perfectly fine to shape a bridge with sandpaper and files, but when it comes to feet, I recommend a knife, for final scraping at least. The smooth surface that a clean knife blade leaves behind cannot be matched with sandpaper.

I sanded feet on a bridge for my violin, and noticed that the sanding marks on the feet actually marred the finish (used fine grit paper too). Granted a bridge is going to wear the top, I'd rather not expedite the process.

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Like everything in the world that can be done more than one way, success usually comes down to the forethought and skill of the operator rather than some inherently superior method. I use sandpaper in conjunction with a custom sanding jig, and quite frankly, as far as accomplishing the ideal fit, I believe my fitting is as perfect as can possibly be realized, by any method.

The problem you had with marring the finish after using sandpaper is real, but not related to the sanded feet per say. Small bits of abrasive will come loose from the sandpaper and remain on the foot surface, thus marring the top. The solution is to simply moisten a q tip or piece of cloth and wipe the feet very well after sanding. I have never had any problem with marring, if the feet have been well cleaned, even when shifting the bridge position. A sanded surface well cleaned is as safe as one cut.

There is a science to sanding the feet well. 220 grit works fine, the thinner the backing the better. I do not like the commercial sanding jigs as they are unstable, and this may be why some people have difficulty getting good results. One needs to make a custom jig. Two feet appropriated from a Kun rest and mounted on a piece of wood can act as a brace that sits across the widest part of the lower bouts. A dowel is fashioned so that it has screws and a mounting plate to hold the bridge on one end. The dowel acts as a guide and is reciprocated almost like a pool cue in a groove or stop mounted on the brace. The Kun feet allow adjustments of the angle of inclination. I think it is better in at least one way since the bridge angle can be controlled with great precision.

Hatch marks applied with a pencil at the outset can help show areas that can be roughed away more quickly with a knife, alternating with brief sanding passes.

The rig was cobbled together just for the picture. Normally, I do some cutting of the ankles before doing the feet. I have similar but larger braces for cello and bass.

A knife is clearly the method of choice for most, but sanding is a viable and very effective alternative when well executed.

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The theory behind the sanding jig seems OK, and I'm sure one can get very satisfactory results with it.

But, it will depend on the topography of the top. On many violins it won't work, but on a double bass it might be different.

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With a simpler version, I replace the sandpaper with a small sheet of paper on which I rub pencil lead.

This provides consistent positioning to mark the high spots which are then removed with a knife.

Your procedure is different, but the result is identical to my using a pencil to apply hatch marks to the foot bottom, except that the high spots are reversed, like a negative photo.

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But, it will depend on the topography of the top. On many violins it won't work, but on a double bass it might be different.

My experience has been that since this jig's horizontal movement is very stable and based on a fixed plane unrelated to the curvature of the top (unlike commercial jigs with their reduced stability and local orientation) one can get very satisfactory results even for violins with foot indentations by working at a clean spot just north or just south of the damage. The geometry is almost always agreeable at one of these locations to provide a foot profile that is well suited to that one position for which there is often little alternative due to damage.

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"Very clever jig, GMM."

I think I have come up with some interesting jigs and other things in my day, but I am not certain this was one of them. I have vague recollections of seeing this idea or something similar in an MN thread a long time ago, or at least enough of an idea to propel me to contrive the current version.

It might have come from seeing a commercial jig and modifying its function. I wish I knew, it would be nice to be able to claim origin with a clear conscience.

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quote:


Originally posted by:
Janito

This jig is icy.

With a simpler version, I replace the sandpaper with a small sheet of paper on which I rub pencil lead.

This provides consistent positioning to mark the high spots which are then removed with a knife.

We used to use carbon paper (does this exist any more? ) to start out with on newer instruments that didn't have depressions under the feet, then switch to chalk if the carbon paper was bridging any low spots.

Traditional methods, and those used in most high-end shops are to use colored chalk powder patted on, or some kind of high-pigment crayon (water soluble are available at art supply stores for easier cleanup) and do all the fitting with a knife. I sometimes follow up with a scraper.

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"Traditional methods, and those used in most high-end shops are to use colored chalk powder patted on, or some kind of high-pigment crayon (water soluble are available at art supply stores for easier cleanup) and do all the fitting with a knife. I sometimes follow up with a scraper. "

David, can you please explain this further.

Where is the chalk/crayon applied?

Do you 'hollow' the contact surface of the foot?

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GMM22 that is great. I have fit the bridge with 220 sand but only

with mi hands.It´s my first bridge and I think the result is

quite good. I think the great surface of thebass bridge helps to do

without a jig, but of course Will be easier with it.GMM22, Would be

posible to show the bass jig? It´d be of great help for

making one.Thank you!!!

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"""""""Traditional methods, and those used in most high-end shops

are to use colored chalk powder patted on, or some kind of

high-pigment crayon (water soluble are available at art supply

stores for easier cleanup) and do all the fitting with a knife. I

sometimes follow up with a scraper. """""""""""

This reminded me that I've heard of bass makers using lipstick on

their bellies to fit the bridge.

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Hi Fernando,

I could, but it is the same except it has much longer pieces of wood and there is a taller block of wood on the square wood since the bridge is much taller than on a violin. I used a picture of a violin because I do not have a bass right now to show a picture of how it works. Do not worry about copying exactly. Just use the same ideas of my device for your own bigger one and you will be fine. If you still have a problem after trying, I will post a picture. Best wishes for your new bridge jig

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quote:


Originally posted by:
Janito

David, can you please explain this further.

Where is the chalk/crayon applied?

Do you 'hollow' the contact surface of the foot?

Chalk or crayon is applied to the violin top. Bridge is set in place and moved slightly to pick up a mark. Where the surface of the top is very uneven, the movement might just be a light tap with a knife handle...barely perceptible movement. Marked area is cut away with a knife.

Another way is to tap downward on the bridge instead of moving the bridge, as you might do to pick up a chalk mark when fitting a patch.

No, I don't hollow the contact surface of the foot.

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Thanks

This is helpful.

I have found that the leaded paper method is satisfactory to get close to final fitting, but then I have had to rely on visual inspection of the feet against a bright light to show up gaps.

I will try the 'crayon-on-body' method next time.

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quote:


Originally posted by:
David Burgess

We used to use carbon paper (does this exist any more?
[/img]
) to start out with on newer instruments that didn't have depressions under the feet, then switch to chalk if the carbon paper was bridging any low spots.

I still have a stash of carbon paper, David.... :-)

What David describes (carbon paper then chalk) is what I generally do... unless the bridge area is really rocky. In that case, I just start out with the chalk.

An additional tip; When transferring the mark (chalk to bridge foot) I generally seat the foot that happens to fit better (and holds the bridge in the correct orientation) and mark, then trim, the opposite foot. Avoids any "twisting" or wobbling that might occur when you're holding the bridge down and trying to get impressions on both feet at once. If you do your trimming correctly, you'll end up alternating feet until the final trimming.

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